1. Field of the Invention
The present invention pertains to methods and devices for determining the metal content of metallic materials, alloys, etc.. In particular, the present invention is concerned with methods and devices used to appraise the precious metal content of jewelry and other articles fabricated from precious metals.
2. Prior Art
In recent years, there has been increasing demand for a means whereby for the sake of improving the efficiency and verity of transactions, dealers in jewelry, precious metals and the like can easily, accurately and at their place of business appraise the metal content and composition of articles fabricated from precious metals. Conventionally, the value of such articles has been appraised using the touchstone method, specific gravity measurement, fire assay method, atomic absorption spectrometry, inductively coupled plasma spectrometry (ICP) and the like. Unfortunately, as will be described below, various problems are associated with each of these methods which render them impractical for accurate appraisal performed at the place of business where transactions in such articles are carried out.
In the case of the touchstone method, a portion of the article to be tested is rubbed against a black quartz test stone whereby a streak is obtained on the test stone which is then treated with acid by which means the composition of the test article can be determined. This test, however, requires a great deal of skill and experience, and furthermore, tends to mar the article being tested. Additionally, this test is not applicable to some white golds (gold - palladium alloys) and platinum alloys which are significantly hard, nor to significantly soft materials such as fine gold or alloys containing more than 92% gold.
Specific gravity determination is an easily performed method in which the weight of the article to be tested is determined while suspended in water. This method, however, can not be used to determine the composition of unknown samples.
The fire assay method, atomic absorption spectrometry, and inductively coupled plasma spectrometry are destructive methods and can therefore not be used on articles for sale.
In view of the above described shortcomings of conventional precious metal appraisal methods, the inventors of the present invention have studied a nondestructive Fluorescence X-ray spectrometry method. In this method, an assay sample is exposed to X-ray radiation, whereby fluorescence X-ray radiation is generated upon which spectral analysis is carried out whereby quantitative analysis of each elemental component can be accomplished simultaneously.
Conventional equipment marketed for carrying out fluorescence X-ray spectrometry, however, requires an assay sample having a homogeneous, and flat and even surface. For this reason, in addition to the difficulty of choosing the best point on the sample to which the analysis is to be directed, because the X-ray beam is of a relatively large diameter (ordinarily 20 mm or greater), small specimens having a complex structure, or specimens made up of a number of different alloys cannot be reliable assayed with such devices. Furthermore, conventional equipment marketed for carrying out fluorescence X-ray spectrometry is quite large and expensive. Thus, not only is a considerable capital investment required, but installation of such a devices consumes a great deal of space when installed in a store or other business cite. Additionally, operation of such a device requires quite specialized knowledge.